HST Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for HST was off by 9.4% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 44% of hours landed within 5% of the reading. Its bias was +5.5%: it ran high on average, an over forecast. The largest miss was 46 MW (61.3%) too high at 4 Sept 2026, 15:00 EDT (UTC-04:00). Dates and times are local (America/New_York).
Key Facts
- The day-ahead demand forecast for HST was off by 9.4% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 44% of hours landed within 5% of the reading. Its bias was +5.5%: it ran high on average, an over forecast. The largest miss was 46 MW (61.3%) too high at 4 Sept 2026, 15:00 EDT (UTC-04:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, HST came 43 (1 is the smallest error).
- On average the forecast differed from reported demand by 8 MW, against average demand of 85 MW.
- The forecast was above reported demand in 62% of compared hours.
Forecast Error at a Glance
695 hours from 21 August to 20 September 2026Average error9.4%
Bias+5.5%
Hours within 5%44%
Worst miss46 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (+4 MW per hour on average): the forecast ran high on average, an over forecast. The worst miss was 46 MW (61.3%) too high at 4 Sept 2026, 15:00 EDT (UTC-04:00): forecast 121 MW, reported 75 MW.
Source: U.S. Energy Information Administration (EIA). (US Government work, public domain) Data as of 2026-09-20. Accuracy is computed by World Power Monitor from the operator's hourly forecast and reported demand.
Forecast and Reported Demand, Last 7 Days
Local time, to 20 Sept 2026, 21:00 EDT (UTC-04:00)Data to 2026-09-20
| Local hour | Reported demand | Day-ahead forecast |
|---|---|---|
| 13 Sept, 22:00 | 85 MW | 94 MW |
| 13 Sept, 23:00 | 76 MW | 87 MW |
| 14 Sept, 00:00 | 69 MW | 75 MW |
| 14 Sept, 01:00 | 63 MW | 70 MW |
| 14 Sept, 02:00 | 60 MW | 67 MW |
| 14 Sept, 03:00 | 58 MW | 59 MW |
| 14 Sept, 04:00 | 58 MW | 57 MW |
| 14 Sept, 05:00 | 60 MW | 57 MW |
| 14 Sept, 06:00 | 62 MW | 57 MW |
| 14 Sept, 07:00 | 60 MW | 56 MW |
| 14 Sept, 08:00 | 60 MW | 65 MW |
| 14 Sept, 09:00 | 65 MW | 75 MW |
| 14 Sept, 10:00 | 75 MW | 86 MW |
| 14 Sept, 11:00 | 85 MW | 95 MW |
| 14 Sept, 12:00 | 95 MW | 106 MW |
| 14 Sept, 13:00 | 104 MW | 110 MW |
| 14 Sept, 14:00 | 106 MW | 100 MW |
| 14 Sept, 15:00 | 110 MW | 95 MW |
| 14 Sept, 16:00 | 113 MW | 91 MW |
| 14 Sept, 17:00 | 114 MW | 93 MW |
| 14 Sept, 18:00 | 113 MW | 97 MW |
| 14 Sept, 19:00 | 111 MW | 96 MW |
| 14 Sept, 20:00 | 110 MW | 99 MW |
| 14 Sept, 21:00 | 103 MW | 96 MW |
| 14 Sept, 22:00 | 95 MW | 90 MW |
| 14 Sept, 23:00 | 87 MW | 86 MW |
| 15 Sept, 00:00 | 78 MW | 86 MW |
| 15 Sept, 01:00 | 73 MW | 81 MW |
| 15 Sept, 02:00 | 69 MW | 77 MW |
| 15 Sept, 03:00 | 66 MW | 70 MW |
| 15 Sept, 04:00 | 65 MW | 70 MW |
| 15 Sept, 05:00 | 67 MW | 71 MW |
| 15 Sept, 06:00 | 69 MW | 72 MW |
| 15 Sept, 07:00 | 66 MW | 69 MW |
| 15 Sept, 08:00 | 69 MW | 70 MW |
| 15 Sept, 09:00 | 77 MW | 78 MW |
| 15 Sept, 10:00 | 85 MW | 85 MW |
| 15 Sept, 11:00 | 93 MW | 87 MW |
| 15 Sept, 12:00 | 101 MW | 97 MW |
| 15 Sept, 13:00 | 107 MW | 104 MW |
| 15 Sept, 14:00 | 110 MW | 107 MW |
| 15 Sept, 15:00 | 114 MW | 112 MW |
| 15 Sept, 16:00 | 118 MW | 113 MW |
| 15 Sept, 17:00 | 118 MW | 115 MW |
| 15 Sept, 18:00 | 117 MW | 114 MW |
| 15 Sept, 19:00 | 115 MW | 113 MW |
| 15 Sept, 20:00 | 113 MW | 109 MW |
| 15 Sept, 21:00 | 106 MW | 106 MW |
| 15 Sept, 22:00 | 97 MW | 100 MW |
| 15 Sept, 23:00 | 89 MW | 93 MW |
| 16 Sept, 00:00 | 83 MW | 86 MW |
| 16 Sept, 01:00 | 76 MW | 81 MW |
| 16 Sept, 02:00 | 71 MW | 77 MW |
| 16 Sept, 03:00 | 69 MW | 70 MW |
| 16 Sept, 04:00 | 68 MW | 70 MW |
| 16 Sept, 05:00 | 69 MW | 71 MW |
| 16 Sept, 06:00 | 70 MW | 72 MW |
| 16 Sept, 07:00 | 66 MW | 69 MW |
| 16 Sept, 08:00 | 69 MW | 70 MW |
| 16 Sept, 09:00 | 78 MW | 77 MW |
| 16 Sept, 10:00 | 87 MW | 85 MW |
| 16 Sept, 11:00 | 96 MW | 94 MW |
| 16 Sept, 12:00 | 103 MW | 102 MW |
| 16 Sept, 13:00 | 107 MW | 107 MW |
| 16 Sept, 14:00 | 111 MW | 111 MW |
| 16 Sept, 15:00 | 116 MW | 116 MW |
| 16 Sept, 16:00 | 119 MW | 118 MW |
| 16 Sept, 17:00 | 120 MW | 120 MW |
| 16 Sept, 18:00 | 120 MW | 118 MW |
| 16 Sept, 19:00 | 116 MW | 117 MW |
| 16 Sept, 20:00 | 111 MW | 115 MW |
| 16 Sept, 21:00 | 105 MW | 106 MW |
| 16 Sept, 22:00 | 96 MW | 97 MW |
| 16 Sept, 23:00 | 87 MW | 87 MW |
| 17 Sept, 00:00 | 78 MW | 76 MW |
| 17 Sept, 01:00 | 73 MW | 77 MW |
| 17 Sept, 02:00 | 69 MW | 72 MW |
| 17 Sept, 03:00 | 67 MW | 70 MW |
| 17 Sept, 04:00 | 66 MW | 70 MW |
| 17 Sept, 05:00 | 66 MW | 70 MW |
| 17 Sept, 06:00 | 68 MW | 71 MW |
| 17 Sept, 07:00 | 65 MW | 67 MW |
| 17 Sept, 08:00 | 69 MW | 71 MW |
| 17 Sept, 09:00 | 73 MW | 77 MW |
| 17 Sept, 10:00 | 74 MW | 88 MW |
| 17 Sept, 11:00 | 73 MW | 97 MW |
| 17 Sept, 12:00 | 73 MW | 104 MW |
| 17 Sept, 13:00 | 73 MW | 109 MW |
| 17 Sept, 14:00 | 75 MW | 112 MW |
| 17 Sept, 15:00 | 81 MW | 116 MW |
| 17 Sept, 16:00 | 88 MW | 119 MW |
| 17 Sept, 17:00 | 92 MW | 121 MW |
| 17 Sept, 18:00 | 95 MW | 122 MW |
| 17 Sept, 19:00 | 96 MW | 117 MW |
| 17 Sept, 20:00 | 97 MW | 114 MW |
| 17 Sept, 21:00 | 92 MW | 106 MW |
| 17 Sept, 22:00 | 85 MW | 97 MW |
| 17 Sept, 23:00 | 78 MW | 90 MW |
| 18 Sept, 00:00 | 70 MW | 79 MW |
| 18 Sept, 01:00 | 65 MW | 74 MW |
| 18 Sept, 02:00 | 62 MW | 64 MW |
| 18 Sept, 03:00 | 59 MW | 63 MW |
| 18 Sept, 04:00 | 59 MW | 62 MW |
| 18 Sept, 05:00 | 60 MW | 63 MW |
| 18 Sept, 06:00 | 63 MW | 68 MW |
| 18 Sept, 07:00 | 60 MW | 66 MW |
| 18 Sept, 08:00 | 61 MW | 69 MW |
| 18 Sept, 09:00 | 69 MW | 75 MW |
| 18 Sept, 10:00 | 79 MW | 81 MW |
| 18 Sept, 11:00 | 89 MW | 88 MW |
| 18 Sept, 12:00 | 95 MW | 94 MW |
| 18 Sept, 13:00 | 92 MW | 100 MW |
| 18 Sept, 14:00 | 89 MW | 105 MW |
| 18 Sept, 15:00 | 88 MW | 108 MW |
| 18 Sept, 16:00 | 83 MW | 110 MW |
| 18 Sept, 17:00 | 83 MW | 111 MW |
| 18 Sept, 18:00 | 87 MW | 112 MW |
| 18 Sept, 19:00 | 89 MW | 110 MW |
| 18 Sept, 20:00 | 88 MW | 107 MW |
| 18 Sept, 21:00 | 86 MW | 101 MW |
| 18 Sept, 22:00 | 81 MW | 95 MW |
| 18 Sept, 23:00 | 75 MW | 90 MW |
| 19 Sept, 00:00 | 68 MW | 71 MW |
| 19 Sept, 01:00 | 63 MW | 66 MW |
| 19 Sept, 02:00 | 59 MW | 62 MW |
| 19 Sept, 03:00 | 57 MW | 61 MW |
| 19 Sept, 04:00 | 55 MW | 60 MW |
| 19 Sept, 05:00 | 55 MW | 60 MW |
| 19 Sept, 06:00 | 56 MW | 64 MW |
| 19 Sept, 07:00 | 55 MW | 62 MW |
| 19 Sept, 08:00 | 59 MW | 65 MW |
| 19 Sept, 09:00 | 64 MW | 76 MW |
| 19 Sept, 10:00 | 70 MW | 87 MW |
| 19 Sept, 11:00 | 76 MW | 97 MW |
| 19 Sept, 12:00 | 86 MW | 105 MW |
| 19 Sept, 13:00 | 91 MW | 99 MW |
| 19 Sept, 14:00 | 92 MW | 96 MW |
| 19 Sept, 15:00 | 101 MW | 99 MW |
| 19 Sept, 16:00 | 104 MW | 103 MW |
| 19 Sept, 17:00 | 105 MW | 107 MW |
| 19 Sept, 18:00 | 100 MW | 109 MW |
| 19 Sept, 19:00 | 93 MW | 104 MW |
| 19 Sept, 20:00 | 89 MW | 102 MW |
| 19 Sept, 21:00 | 85 MW | 98 MW |
| 19 Sept, 22:00 | 80 MW | 92 MW |
| 19 Sept, 23:00 | 74 MW | 87 MW |
| 20 Sept, 00:00 | 68 MW | 69 MW |
| 20 Sept, 01:00 | 63 MW | 64 MW |
| 20 Sept, 02:00 | 59 MW | 60 MW |
| 20 Sept, 03:00 | 56 MW | 57 MW |
| 20 Sept, 04:00 | 54 MW | 56 MW |
| 20 Sept, 05:00 | 54 MW | 56 MW |
| 20 Sept, 06:00 | 55 MW | 57 MW |
| 20 Sept, 07:00 | 55 MW | 57 MW |
| 20 Sept, 08:00 | 59 MW | 60 MW |
| 20 Sept, 09:00 | 66 MW | 63 MW |
| 20 Sept, 10:00 | 71 MW | 67 MW |
| 20 Sept, 11:00 | 80 MW | 74 MW |
| 20 Sept, 12:00 | 92 MW | 78 MW |
| 20 Sept, 13:00 | 100 MW | 84 MW |
| 20 Sept, 14:00 | 100 MW | 89 MW |
| 20 Sept, 15:00 | 95 MW | 95 MW |
| 20 Sept, 16:00 | 92 MW | 98 MW |
| 20 Sept, 17:00 | 84 MW | 100 MW |
| 20 Sept, 18:00 | 81 MW | 101 MW |
| 20 Sept, 19:00 | 83 MW | 99 MW |
| 20 Sept, 20:00 | 83 MW | 95 MW |
| 20 Sept, 21:00 | 80 MW | 91 MW |
Assumptions
- Only hours with both a forecast and a positive demand reading count (695 of 720 hours in the window). Missing and zero values, and readings under 30% or over 3 times the grid's own median for the window, are treated as reporting faults and left out.
- Error is (forecast minus reported demand) divided by reported demand; average error uses absolute values so high and low misses do not cancel. Bias keeps the sign and does cancel.
- Reported demand is preliminary and may be revised. A 30 day window is a short sample and one heat wave or holiday can move these figures.
- US figures are for the EIA balancing authority or region named on this page. US and European grids are ranked separately.